1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to a method and system for controlling power in a communication system using a hybrid duplexing scheme.
2. Description of the Related Art
The next generation communication system focuses on supporting a voice service as well as multimedia services having various traffic characteristics, such as the broadcasting and the real-time videoconference. Therefore, in order to efficiently provide the services having the various characteristics, there is a need for a duplexing scheme that considers asymmetry and continuity of uplink/downlink transmission according to service characteristics.
Additionally, the next generation wireless communication system should enable variable asymmetrical services that efficiently provide multimedia traffics, and should also have a characteristic capable of providing high-speed data transmission with high reliability. The term “asymmetrical service” refers to a service in which a DownLink (DL) and an UpLink (UL) are different in data rate. The multimedia traffics need a higher data rate in the DL rather than the UL, because a Mobile Station (MS) having both mobility and fixity receives multimedia services. Preferably, a ratio of the asymmetry is subject to change.
The duplexing scheme used in the wireless communication system can be classified into a Time Division Duplexing (TDD) scheme and a Frequency Division Duplexing (FDD) scheme. The TDD scheme divides the same frequency band into time intervals and alternately switches transmission intervals and reception intervals, thereby implementing bi-directional communication. The FDD scheme divides a given frequency band into transmission bands and reception bands, thereby performing bi-directional communication.
In the TDD-based communication system, a Base Station (BS) can allocate some or all of its available time slots to MSs, and asymmetrical communication is possible through variable allocation of the time slots. However, in the TDD-based communication system, if a radius of a cell managed by the BS increases, a guard time between transmission/reception time slots increases due to a round-trip delay, decreasing transmission efficiency. Therefore, in a large-cell radius communication environment, or in the macro-cell communication environment, it is not preferable to use the TDD scheme. Further, in the TDD-based communication system, because the asymmetry ratio of each cell is not constant in the multi-cell environment, considerable frequency interference occurs between MSs located in the boundary between neighbor cells.
However, in the FDD-based communication system, time delay for transmission/reception does not occur because transmission frequency bands are separated from reception frequency bands. Therefore, there is no round-trip delay caused by the time delay, thus, the FDD-based communication system is suitable for the large-cell radius environment like the macro-cell environment. However, the FDD-based communication system is not suitable for duplexing for variable asymmetrical transmission because the transmission frequency bands and the reception frequency bands are fixed.
Accordingly, there is a demand for research into hybrid duplexing schemes that can obtain the merits of both of the TDD scheme and the FDD scheme by mixing the two duplexing schemes taking into account various communication environments and traffic characteristics of the next generation communication system. In order to meet the demand, a communication system using a hybrid duplexing scheme has been proposed, and the communication system using the hybrid duplexing scheme operates based on the TDD scheme in the micro-cell environment, and operates based on the FDD scheme in the macro-cell environment.
However, when the communication system using the hybrid duplexing scheme operates based on one of the TDD scheme and the FDD scheme according to communication environment, a level of the power that the BS transmits to MSs varies according to the communication environment. The variation in the transmission power according to the communication environment may decrease system performance, which is considerable, particularly when the communication system operates based on the TDD scheme.